Hydroconversion processes are important in the modern world in providing important basic fuels for everyday life. As it becomes of an increasing necessity to utilize heavier crude oil feedstocks, the oil refining industry has turned to hydrocracking processes to provide the lighter basic fuels which modern society demands. In certain regions, e.g. North America, the lighter liquid products boiling below 191° C. are more in demand than middle distillate products. Such lighter products are called the naphtha fractions, with heavy naphtha (the fraction boiling from 82° C. to 191° C.) being particularly desirable. There has been considerable effort devoted to the development of hydrocracking catalysts which combine high naphtha selectivity with a low tendency to overcrack towards light products, in particular to the less valuable C1-C3 and C4 gaseous by-products, in combination with limited hydrogenation of aromatic rings.
Naphtha preferably has a high amount of aromatics as this gives a high octane number for the gasoline derived from it. A further advantage of less aromatics hydrogenation is that less hydrogen is consumed which is attractive from a process operation point of view. Limited hydrogenation and the resulting high aromatics content is not easily achieved as the hydrocracking catalyst preferably has a high hydrogenation activity in order to prevent overcracking of the feedstock.
Metal containing impregnating solutions for preparing metal containing catalysts are typically highly concentrated and stabilized by a diverse range of inorganic as well as organic additives such as citric acid. US 2005/0179249 describes impregnation solutions comprising metal-containing compounds and a chelating agent such as citric acid for the manufacture of diesel selective hydrocracking catalyst comprising a shaped catalyst carrier containing ultrastable zeolite Y or very ultrastable zeolite Y having a unit cell size less than 24.40 Å and a SAR preferably in the range of from 20 to 100 and from 3 to 5% wt of nickel and molybdenum in an amount in the range of from 6 to 18% wt, preferably 10 to 15% wt, or tungsten in an amount in the range of from 10 to 25% wt, preferably 15 to 22% wt.
WO 2011/067258 relates to the manufacture of zeolite for use in naphtha-selective catalyst compositions containing from 5 to 30, especially 5 to 10, of Group VI metal(s) and/or from 1 to 5 parts by weight of Group VIII metal(s), calculated as metal per 100 parts by weight (dry weight) of total catalyst composition. The zeolite has a unit cell size in the range of from 24.42 to 24.52 Å, a bulk silica to alumina molar ratio (SAR) in the range of from 10 to 15 and a surface area of from 910 to 1020 m2/g.